Résumé
Co‐evolution is expected to result in correlations of character states when measured in several species. Comparative analysis constitutes a natural method of investigation to exhibit coevolving traits. Traits can be measured at the leaves of the tree, representing a sample of species with partially shared histories. Once the traits are measured in the different species, one can compute simple correlations between the trait values. To demonstrate correlated evolution between two traits, one has to reject the statistical independence between the two processes that govern the evolution of the two traits. This chapter shows how standard classical genetics can be rethought in terms of correlated evolution between phenotypic trait(s) and molecular trait(s) in the genome. It suggests that the whole history of gene mapping, since its very beginning, can be included in the large view of correlated evolution. Genetic sequences can be viewed as traits with simple, well‐defined discrete states.